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		<p class="post-meta">
		<time class="dt-published" datetime="2020-03-12T00:00:00-04:00" itemprop="datePublished">Thursday, March 12, 2020
		</time>• by <span itemprop="author" itemscope itemtype="http://schema.org/Person"><span class="p-author h-card" itemprop="name">Ron Tarrant</span></span></p>
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		<h1 id="0104-widget-opacity-ii--real-ghosting-and-more-real-ghosting">0104: Widget Opacity II – Real Ghosting and More Real Ghosting</h1>

<p>Last time, we looked at how to fake ghosting using the <code class="language-plaintext highlighter-rouge">setOpacity()</code> function. This time, we’ll see how to do proper ghosting using the <code class="language-plaintext highlighter-rouge">setSensitive()</code> function. Then we’ll move on to an example wherein we overlay buttons, one ghosted and one not, over an image. And we’ll be using a <code class="language-plaintext highlighter-rouge">Layout</code> instead of a <code class="language-plaintext highlighter-rouge">Grid</code> this time.</p>

<h2 id="how-to-make-a-cruel-widget">How to Make a Cruel Widget</h2>

<!-- 0, 1 -->
<!-- first occurrence of application and terminal screen shots on a single page -->
<div class="screenshot-frame">
	<div class="frame-header">
		Results of this example:
	</div>
	<div class="frame-screenshot">
		<figure>
			<img id="img0" src="../images/screenshots/016_sfx/sfx_07.png" alt="Current example output" />		<!-- img# -->
			
			<!-- Modal for screenshot -->
			<div id="modal0" class="modal">																	<!-- modal# -->
				<span class="close0">&times;</span>															<!-- close# -->
				<img class="modal-content" id="img00" />															<!-- img## -->
				<div id="caption"></div>
			</div>
			
			<script>
			// Get the modal
			var modal = document.getElementById("modal0");														// modal#
			
			// Get the image and insert it inside the modal - use its "alt" text as a caption
			var img = document.getElementById("img0");															// img#
			var modalImg = document.getElementById("img00");													// img##
			var captionText = document.getElementById("caption");

			img.onclick = function()
			{
			  modal.style.display = "block";
			  modalImg.src = this.src;
			  captionText.innerHTML = this.alt;
			}
			
			// Get the <span> element that closes the modal
			var span = document.getElementsByClassName("close0")[0];											// close#
			
			// When the user clicks on <span> (x), close the modal
			span.onclick = function()
			{ 
				modal.style.display = "none";
			}
			</script>
			<figcaption>
			Current example output
			</figcaption>
		</figure>
	</div>

	<div class="frame-terminal">
		<figure class="right">
			<img id="img1" src="../images/screenshots/016_sfx/sfx_07_term.png" alt="Current example terminal output" />		<!-- img#, filename -->

			<!-- Modal for terminal shot -->
			<div id="modal1" class="modal">																				<!-- modal# -->
				<span class="close1">&times;</span>																		<!-- close# -->
				<img class="modal-content" id="img11" />																		<!-- img## -->
				<div id="caption"></div>
			</div>
			
			<script>
			// Get the modal
			var modal = document.getElementById("modal1");																	// modal#
			
			// Get the image and insert it inside the modal - use its "alt" text as a caption
			var img = document.getElementById("img1");																		// img#
			var modalImg = document.getElementById("img11");																// img##
			var captionText = document.getElementById("caption");

			img.onclick = function()
			{
			  modal.style.display = "block";
			  modalImg.src = this.src;
			  captionText.innerHTML = this.alt;
			}
			
			// Get the <span> element that closes the modal
			var span = document.getElementsByClassName("close1")[0];														// close#
			
			// When the user clicks on <span> (x), close the modal
			span.onclick = function()
			{ 
				modal.style.display = "none";
			}
			</script>

			<figcaption>
				Current example terminal output (click for enlarged view)
			</figcaption>
		</figure>
	</div>

	<div class="frame-footer">																								<!-- ------------- filename (below) --------- -->
		The code file for this example is available <a href="https://github.com/rontarrant/gtkd_demos/blob/master/016_sfx/sfx_07_insensitive.d" target="_blank">here</a>.
	</div>
</div>
<!-- end of snippet for first (1st) occurrence of application and terminal screen shots on a single page -->

<p>Well, not exactly cruel… just insensitive.</p>

<p>Last time, it took more code to get this job done. For one thing, <code class="language-plaintext highlighter-rouge">MySwitch</code> needed a ghosting flag to keep track of when the opacity was low. And for another, we needed an entire function (<code class="language-plaintext highlighter-rouge">switchGhosting</code>) so <code class="language-plaintext highlighter-rouge">MyButton</code> could turn ghosting on and off.</p>

<p>But this time, we eliminate both of these. <code class="language-plaintext highlighter-rouge">MyButton</code>, because it has <code class="language-plaintext highlighter-rouge">MySwitch</code> set up as a companion (like we did last time) can go straight for the jugular:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">bool</span> <span class="n">onButtonPress</span><span class="p">(</span><span class="n">Event</span> <span class="n">e</span><span class="p">,</span> <span class="n">Widget</span> <span class="n">w</span><span class="p">)</span>
<span class="p">{</span>
	<span class="k">if</span><span class="p">(</span><span class="n">companion</span><span class="p">.</span><span class="n">getSensitive</span><span class="p">()</span> <span class="k">is</span> <span class="kc">false</span><span class="p">)</span>
	<span class="p">{</span>
		<span class="n">writeln</span><span class="p">(</span><span class="s">"Activating switch"</span><span class="p">);</span>
		<span class="n">companion</span><span class="p">.</span><span class="n">setSensitive</span><span class="p">(</span><span class="kc">true</span><span class="p">);</span>
		<span class="n">setLabel</span><span class="p">(</span><span class="n">labelText</span><span class="p">[</span><span class="mi">1</span><span class="p">]);</span>
	<span class="p">}</span>
	<span class="k">else</span>
	<span class="p">{</span>
		<span class="n">writeln</span><span class="p">(</span><span class="s">"Deactivating switch."</span><span class="p">);</span>
		<span class="n">companion</span><span class="p">.</span><span class="n">setSensitive</span><span class="p">(</span><span class="kc">false</span><span class="p">);</span>
		<span class="n">setLabel</span><span class="p">(</span><span class="n">labelText</span><span class="p">[</span><span class="mi">0</span><span class="p">]);</span>
	<span class="p">}</span>
		
	<span class="k">return</span><span class="p">(</span><span class="kc">true</span><span class="p">);</span>
		
<span class="p">}</span> <span class="c1">// onButtonPress()</span>
</code></pre></div></div>

<p>It checks to see which way <code class="language-plaintext highlighter-rouge">MySwitch</code>’s sensitivity is set and flips it to the other state. Because we’re doing it this way, the opacity of the <code class="language-plaintext highlighter-rouge">Label</code> isn’t going to match <code class="language-plaintext highlighter-rouge">MySwitch</code>’s insensitive state. This may be confusing for the user, so syncing the <code class="language-plaintext highlighter-rouge">Label</code>’s appearance with that of <code class="language-plaintext highlighter-rouge">MySwitch</code> may be something to try as an exercise.</p>

<p>Or not.</p>

<p>Moving right along…</p>

<p>The only other difference between this example and <a href="https://github.com/rontarrant/gtkd_demos/blob/master/016_sfx/sfx_06_opacity_ghosting.d">the last one</a> is that the only object that knows about the <code class="language-plaintext highlighter-rouge">Label</code> is the <code class="language-plaintext highlighter-rouge">ButtonGrid</code>, so all references to <code class="language-plaintext highlighter-rouge">Label</code> outside of <code class="language-plaintext highlighter-rouge">ButtonGrid</code> are now eliminated.</p>

<h2 id="ghosted-buttons-on-an-image">Ghosted Buttons on an Image</h2>

<!-- 2, 3 -->
<!-- second occurrence of application and terminal screen shots on a single page -->
<div class="screenshot-frame">
	<div class="frame-header">
		Results of this example:
	</div>
	<div class="frame-screenshot">
		<figure>
			<img id="img2" src="../images/screenshots/016_sfx/sfx_08.png" alt="Current example output" />		<!-- img# -->
			
			<!-- Modal for screenshot -->
			<div id="modal2" class="modal">																<!-- modal# -->
				<span class="close2">&times;</span>														<!-- close# -->
				<img class="modal-content" id="img22" />														<!-- img## -->
				<div id="caption"></div>
			</div>
			
			<script>
			// Get the modal
			var modal = document.getElementById("modal2");													// modal#
			
			// Get the image and insert it inside the modal - use its "alt" text as a caption
			var img = document.getElementById("img2");														// img#
			var modalImg = document.getElementById("img22");												// img##
			var captionText = document.getElementById("caption");

			img.onclick = function()
			{
			  modal.style.display = "block";
			  modalImg.src = this.src;
			  captionText.innerHTML = this.alt;
			}
			
			// Get the <span> element that closes the modal
			var span = document.getElementsByClassName("close2")[0];										// close#
			
			// When the user clicks on <span> (x), close the modal
			span.onclick = function()
			{ 
				modal.style.display = "none";
			}
			</script>
			<figcaption>
			Current example output
			</figcaption>
		</figure>
	</div>

	<div class="frame-terminal">
		<figure class="right">
			<img id="img3" src="../images/screenshots/016_sfx/sfx_08_term.png" alt="Current example terminal output" /> 		<!-- img#, filename -->

			<!-- Modal for terminal shot -->
			<div id="modal3" class="modal">																			<!-- modal# -->
				<span class="close3">&times;</span>																	<!-- close# -->
				<img class="modal-content" id="img33" />																	<!-- img## -->
				<div id="caption"></div>
			</div>
			
			<script>
			// Get the modal
			var modal = document.getElementById("modal3");																// modal#
			
			// Get the image and insert it inside the modal - use its "alt" text as a caption
			var img = document.getElementById("img3");																	// img#
			var modalImg = document.getElementById("img33");															// img##
			var captionText = document.getElementById("caption");

			img.onclick = function()
			{
			  modal.style.display = "block";
			  modalImg.src = this.src;
			  captionText.innerHTML = this.alt;
			}
			
			// Get the <span> element that closes the modal
			var span = document.getElementsByClassName("close3")[0];													// close#
			
			// When the user clicks on <span> (x), close the modal
			span.onclick = function()
			{ 
				modal.style.display = "none";
			}
			</script>

			<figcaption>
				Current example terminal output (click for enlarged view)
			</figcaption>
		</figure>
	</div>

	<div class="frame-footer">																							<!--------- filename (below) ------------>
		The code file for this example is available <a href="https://github.com/rontarrant/gtkd_demos/blob/master/016_sfx/sfx_08_ghost_over_drawingarea.d" target="_blank">here</a>.
	</div>
</div>
<!-- end of snippet for second (2nd) occurrence of application and terminal screen shots on a single page -->

<p>There may be nothing inherently new in this demo, but it is another way to demonstrate what we’re talking about as well as present another possible use case. Here is a list of what’s being demonstrated here:</p>

<ul>
  <li>an opacity-ghosted <code class="language-plaintext highlighter-rouge">Button</code> can be active,</li>
  <li>an insensitive <code class="language-plaintext highlighter-rouge">Button</code> can’t, and</li>
  <li>making a <code class="language-plaintext highlighter-rouge">Button</code> insensitive doesn’t change its opacity.</li>
</ul>

<p>And since we’re using a Layout instead of a <code class="language-plaintext highlighter-rouge">Grid</code>, let’s look at how all this fits together…</p>

<h3 id="the-bglayout-class">The BGLayout Class</h3>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">class</span> <span class="n">BGLayout</span> <span class="p">:</span> <span class="n">Layout</span>
<span class="p">{</span>
	<span class="n">MyButton</span> <span class="n">myButton1</span><span class="p">,</span> <span class="n">myButton2</span><span class="p">,</span> <span class="n">myButton3</span><span class="p">;</span>
	<span class="n">BGDrawingArea</span> <span class="n">bgDrawing</span><span class="p">;</span>
	
	<span class="k">this</span><span class="p">()</span>
	<span class="p">{</span>
		<span class="k">super</span><span class="p">(</span><span class="kc">null</span><span class="p">,</span> <span class="kc">null</span><span class="p">);</span>
		<span class="n">setSizeRequest</span><span class="p">(</span><span class="mi">640</span><span class="p">,</span> <span class="mi">426</span><span class="p">);</span> <span class="c1">// has to be set so signals get through from child widgets</span>
		
		<span class="n">bgDrawing</span> <span class="p">=</span> <span class="k">new</span> <span class="n">BGDrawingArea</span><span class="p">();</span>
		<span class="n">put</span><span class="p">(</span><span class="n">bgDrawing</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span>		
		
		<span class="n">myButton1</span> <span class="p">=</span> <span class="k">new</span> <span class="n">MyButton</span><span class="p">(</span><span class="mi">0</span><span class="p">);</span>
		<span class="n">put</span><span class="p">(</span><span class="n">myButton1</span><span class="p">,</span> <span class="mi">226</span><span class="p">,</span> <span class="mi">213</span><span class="p">);</span>
		<span class="n">myButton1</span><span class="p">.</span><span class="n">setOpacity</span><span class="p">(</span><span class="mf">0.5</span><span class="p">);</span>

		<span class="n">myButton2</span> <span class="p">=</span> <span class="k">new</span> <span class="n">MyButton</span><span class="p">(</span><span class="mi">1</span><span class="p">);</span>
		<span class="n">put</span><span class="p">(</span><span class="n">myButton2</span><span class="p">,</span> <span class="mi">320</span><span class="p">,</span> <span class="mi">120</span><span class="p">);</span>

		<span class="n">myButton3</span> <span class="p">=</span> <span class="k">new</span> <span class="n">MyButton</span><span class="p">(</span><span class="mi">2</span><span class="p">);</span>
		<span class="n">put</span><span class="p">(</span><span class="n">myButton3</span><span class="p">,</span> <span class="mi">175</span><span class="p">,</span> <span class="mi">306</span><span class="p">);</span>
		<span class="n">myButton3</span><span class="p">.</span><span class="n">setSensitive</span><span class="p">(</span><span class="kc">false</span><span class="p">);</span>
		
	<span class="p">}</span> <span class="c1">// this()</span>
	
<span class="p">}</span> <span class="c1">// class BGLayout</span>
</code></pre></div></div>

<p>Because we want to place these <code class="language-plaintext highlighter-rouge">Button</code>s over parts of the image that will show through, thus proving the transparency of the <code class="language-plaintext highlighter-rouge">Button</code>s, we’re using a <code class="language-plaintext highlighter-rouge">Layout</code> so we don’t have to fiddle around too much when placing them.</p>

<p>Notice also that each call to <code class="language-plaintext highlighter-rouge">MyButton()</code> passes in a number. This is the index into the <code class="language-plaintext highlighter-rouge">labelText</code> array in the <code class="language-plaintext highlighter-rouge">MyButton</code> class and decides which of the three strings we’ll use initially for labeling the <code class="language-plaintext highlighter-rouge">Button</code>s.</p>

<h3 id="the-mybutton-class">The MyButton Class</h3>

<p>Here’s the preamble where the <code class="language-plaintext highlighter-rouge">labelText</code> string array is defined:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nb">string</span><span class="p">[]</span> <span class="n">labelText</span> <span class="p">=</span> <span class="p">[</span><span class="s">"Ghosted"</span><span class="p">,</span> <span class="s">"Non-ghosted"</span><span class="p">,</span> <span class="s">"Insensitive"</span><span class="p">];</span>
</code></pre></div></div>

<h4 id="the-constructor">The Constructor</h4>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">this</span><span class="p">(</span><span class="kt">int</span> <span class="n">labelIndex</span><span class="p">)</span>
<span class="p">{</span>
	<span class="k">super</span><span class="p">(</span><span class="n">labelText</span><span class="p">[</span><span class="n">labelIndex</span><span class="p">]);</span>
	<span class="n">addOnButtonPress</span><span class="p">(&amp;</span><span class="n">onButtonPress</span><span class="p">);</span>

<span class="p">}</span> <span class="c1">// this()</span>
</code></pre></div></div>

<p>Just pick the label string and hook up the signal.</p>

<h4 id="the-callback">The Callback</h4>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="kt">bool</span> <span class="n">onButtonPress</span><span class="p">(</span><span class="n">Event</span> <span class="n">e</span><span class="p">,</span> <span class="n">Widget</span> <span class="n">w</span><span class="p">)</span>
<span class="p">{</span>
	<span class="k">if</span><span class="p">(</span><span class="n">getOpacity</span><span class="p">()</span> <span class="p">!</span><span class="k">is</span> <span class="mf">1.0</span><span class="p">)</span>
	<span class="p">{</span>
		<span class="n">setLabel</span><span class="p">(</span><span class="n">labelText</span><span class="p">[</span><span class="mi">1</span><span class="p">]);</span>
		<span class="n">setOpacity</span><span class="p">(</span><span class="mf">1.0</span><span class="p">);</span>
		<span class="n">writeln</span><span class="p">(</span><span class="s">"opacity = "</span><span class="p">,</span> <span class="n">getOpacity</span><span class="p">(),</span> <span class="s">", turning it to full."</span><span class="p">);</span>
	<span class="p">}</span>
	<span class="k">else</span>
	<span class="p">{</span>
		<span class="n">setLabel</span><span class="p">(</span><span class="n">labelText</span><span class="p">[</span><span class="mi">0</span><span class="p">]);</span>
		<span class="n">setOpacity</span><span class="p">(</span><span class="mf">0.5</span><span class="p">);</span>
		<span class="n">writeln</span><span class="p">(</span><span class="s">"opacity = "</span><span class="p">,</span> <span class="n">getOpacity</span><span class="p">(),</span> <span class="s">", turning it to half."</span><span class="p">);</span>
	<span class="p">}</span>
	<span class="n">writeln</span><span class="p">(</span><span class="s">"Button pressed is: "</span><span class="p">,</span> <span class="n">getLabel</span><span class="p">());</span>
	
	<span class="k">return</span><span class="p">(</span><span class="kc">true</span><span class="p">);</span>
	
<span class="p">}</span> <span class="c1">// onButtonPress()</span>
</code></pre></div></div>

<p>Here, we check the opacity setting, using an <code class="language-plaintext highlighter-rouge">if</code>/<code class="language-plaintext highlighter-rouge">else</code> to switch back and forth from half opacity to full.</p>

<p>You may wonder why I’ve done it this way, checking to see if opacity is set to <code class="language-plaintext highlighter-rouge">1.0</code>. In fact, you may be tempted to test if it’s set to <code class="language-plaintext highlighter-rouge">0.5</code> (I was at first.). But the reality of the situation is that when you set the opacity to <code class="language-plaintext highlighter-rouge">0.5</code>, it’s actually set to <code class="language-plaintext highlighter-rouge">0.501961</code>. It’s our old buddy FPI (Floating Point Inaccuracy) come to play havoc with our sanity. You could test for <code class="language-plaintext highlighter-rouge">0.501961</code> if you like, but I don’t imagine it’s worth the extra typing. Who knows if the inaccuracy will be the same from one OS to another or between the 32-bit and the 64-bit versions of an OS. It seems more sane to me to test for <code class="language-plaintext highlighter-rouge">1.0</code> instead. Or if you want to deal with finer-tuned numbers, just look for a range like this:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">if</span><span class="p">(</span><span class="n">getOpacity</span><span class="p">()</span> <span class="p">&gt;</span> <span class="mf">0.5</span> <span class="p">&amp;&amp;</span> <span class="n">getOpacity</span><span class="p">()</span> <span class="p">&lt;</span> <span class="mf">0.6</span><span class="p">)</span>
</code></pre></div></div>

<p>Of course, you might also switch based on the <code class="language-plaintext highlighter-rouge">labelText</code>, like this:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">if</span><span class="p">(</span><span class="n">getLabel</span><span class="p">()</span> <span class="p">==</span> <span class="n">labelText</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="p">{</span>
	<span class="n">setLabel</span><span class="p">(</span><span class="n">labelText</span><span class="p">[</span><span class="mi">1</span><span class="p">]);</span>
	<span class="n">setOpacity</span><span class="p">(</span><span class="mf">1.0</span><span class="p">);</span>
	<span class="n">writeln</span><span class="p">(</span><span class="s">"label: "</span><span class="p">,</span> <span class="n">getLabel</span><span class="p">(),</span> <span class="s">", opacity = "</span><span class="p">,</span> <span class="n">getOpacity</span><span class="p">(),</span> <span class="s">", turning it to full."</span><span class="p">);</span>
<span class="p">}</span>
<span class="k">else</span>
<span class="p">{</span>
	<span class="n">setLabel</span><span class="p">(</span><span class="n">labelText</span><span class="p">[</span><span class="mi">0</span><span class="p">]);</span>
	<span class="n">setOpacity</span><span class="p">(</span><span class="mf">0.5</span><span class="p">);</span>
	<span class="n">writeln</span><span class="p">(</span><span class="s">"label: "</span><span class="p">,</span> <span class="n">getLabel</span><span class="p">(),</span> <span class="s">", opacity = "</span><span class="p">,</span> <span class="n">getOpacity</span><span class="p">(),</span> <span class="s">", turning it to half."</span><span class="p">);</span>
<span class="p">}</span>
</code></pre></div></div>

<p>All this does is look to see if the label text is <code class="language-plaintext highlighter-rouge">“Ghosted”</code> and if it is, changes it to <code class="language-plaintext highlighter-rouge">“Non-ghosted”</code>.</p>

<p>Note: You might think you can do a string comparison with the is keyword as in:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">if</span><span class="p">(</span><span class="n">getLabel</span><span class="p">()</span> <span class="k">is</span> <span class="n">labelText</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
</code></pre></div></div>

<p>However, because <em>D</em> uses <em>Unicode</em> strings, we can’t do that, but but we can do this:</p>

<div class="language-d highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="n">getLabel</span><span class="p">()</span> <span class="p">==</span> <span class="n">labelText</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
</code></pre></div></div>

<p>I’ve left both methods in the source with the label comparison commented out so you can (to borrow an expression from my grandmother) pick your choose.</p>

<h2 id="conclusion">Conclusion</h2>

<p>So much for ghosting, opacity, and sensitivity. Next time, we’ll look at some common <em>D-language</em> stuff that you may find useful in building a UI, even though these snippets aren’t necessarily <em>GTK</em>-specific.</p>

<p>Until then, have a happy life.</p>

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